Nanostructure based display devices

ABSTRACT

A display device includes a backlight unit having a light source and a liquid crystal display (LCD) module. The light source is configured to emit a primary light in a first wavelength region. The LCD module includes a pixel having a first, second, and third sub-pixels. The first sub-pixel includes a first emissive surface configured to emit a first light in a second wavelength region. The second sub-pixel includes a second emissive surface configured to emit a second light in a third wavelength region. The third sub-pixel includes a third emissive surface configured to emit a third light in the first wavelength region. The third luminance is greater than the first luminance and the second luminance. An area of the third emissive surface is smaller than an area of the first emissive surface and an area of the second emissive surface.

CROSS REFERENCE TO RELATED APPLICATIONS

This application incorporates by reference in their entirety U.S.Provisional Appl. No. 62/550,384, filed Aug. 25, 2017.

BACKGROUND OF THE INVENTION Field

The present invention relates to display devices including phosphorfilms having luminescent nanostructures such as quantum dots (QDs).

Background

Luminescent nanostructures (NSs) such as quantum dots (QDs) represent aclass of phosphors that have the ability to emit light at a singlespectral peak with narrow line width, creating highly saturated colors.It is possible to tune the emission wavelength based on the size of theNSs. The NSs are used to produce a NS film. That may be used as a colordown conversion layer in display devices (e.g., liquid crystal display(LCD) device, organic light emitting diode (OLED) display device). Theuse of a color down conversion layer in emissive displays can improvethe system efficiency by down-converting white light, blue light, orultra-violet (UV) light to a more reddish light, greenish light, or bothbefore the light passes through a color filter. This use of a color downconversion layer may reduce loss of light energy due to filtering.

NSs may be used as the conversion material due to their broad absorptionand narrow emission spectra. Because, the density of NSs required forsuch application is very high in a very thin color down conversion layerof about 3 μm-6 μm, NSs prepared using current methods suffer fromquenching of their optical properties when the NSs are closely packednext to each other in a thin NS film. As such, current NS-based displaydevices using NS films as color down conversion layers suffer from lowquantum yield (QY).

One of the factors used to define the image quality of a display deviceis the color gamut coverage of standard RGB color spaces such as Rec.2020, Rec. 709, DCI P3, NTSC, or sRGB provided by the display device.FIG. 1 illustrates a definition of color gamut coverage of a displaydevice. In FIG. 1, area 101 formed between 1976 CIE color coordinates101 a-101 c represents the color gamut of a standard RGB color space(e.g., Rec. 2020) on the 1976 CIE u′-v′ chromaticity diagram 100. Area102 formed between 1976 CIE color coordinates 102 a-102 c represents thecolor gamut of the display device on the 1976 CIE u′-v′ chromaticitydiagram 100. Color gamut coverage of the display device may be definedas a ratio of the overlapping area 103 between areas 101 and 102 to area101. The wider the color gamut coverage of a display device, the wideris the range of colors identifiable by the human eye (i.e., the visiblespectrum) rendered by the display device, and hence, improves the imagequality of the display device assuming the other factors contributing tothe image quality are optimized.

Current display devices suffer from a trade-off between achieving thedesired brightness (e.g., brightness required by high dynamic range(HDR) imaging standards) and the desired color gamut coverage (e.g.,greater than 85%) of the standard RGB color spaces. For example, somedisplay devices suffer about 30% loss in brightness to achieve over 90%DCI P3 color gamut coverage. Hence, with current technology, loss ofbrightness in display devices would be significantly higher in order toachieve color gamut coverage of color spaces that are even wider thanDCI P3 (e.g., Rec. 2020).

Another disadvantage suffered by current display devices is the leakageof unconverted light through conversion materials (e.g., NS films) ofthe display devices that negatively affects the color gamut coverage ofthe display devices. For example, some display devices suffer fromleakage of unwanted blue light through their green and/or red pixels.This may occur when blue light incident on the conversion material froma blue light source is not fully absorbed and converted into greenand/or red light by the conversion material.

SUMMARY

Accordingly, there is need for display devices with improved color gamutcoverage and with less of a trade-off between achieving the desiredcolor gamut coverage of the wide RGB color spaces and the desiredbrightness.

According to an embodiment, a display device includes a backlight unithaving a light source and a liquid crystal display (LCD) module. Thelight source is configured to emit a primary light in a first wavelengthregion of an electromagnetic (EM) spectrum. The LCD module includes apixel having first, second, and third sub-pixels. The first sub-pixelincludes a first emissive surface configured to emit a first light,having a first amount of total luminance, in a second wavelength regionof the EM spectrum. The second sub-pixel includes a second emissivesurface configured to emit a second light, having a second amount oftotal luminance, in a third wavelength region of the EM spectrum. Thethird sub-pixel includes a third emissive surface configured to emit athird light, having a third amount of total luminance, in the firstwavelength region of the EM spectrum. The first, second, and thirdwavelength regions are different from each other. The third luminance isgreater than the first luminance and the second luminance. An area ofthe third emissive surface is smaller than an area of the first emissivesurface and an area of the second emissive surface.

According to an embodiment, a display device includes first, second, andthird sub-pixels. The first sub-pixel includes a first emissive surfaceconfigured to emit a first light, having a first amount of totalluminance, in a first wavelength region of the EM spectrum. The secondsub-pixel includes a second emissive surface configured to emit a secondlight, having a second amount of total luminance, in a second wavelengthregion of the EM spectrum. The third sub-pixel includes a third emissivesurface configured to emit a third light, having a third amount of totalluminance, in a third wavelength region of the EM spectrum. The first,second, and third wavelength regions are different from each other. Thethird luminance is greater than the first luminance and the secondluminance. An area of the third emissive surface is smaller than an areaof the first emissive surface and an area of the second emissivesurface.

According to an embodiment, a display device includes first, second, andthird emissive surfaces. The first emissive surface configured to emit afirst light, having a first amount of total luminance, in a firstwavelength region of the EM spectrum. The second emissive surfaceconfigured to emit a second light, having a second amount of totalluminance, in a second wavelength region of the EM spectrum. The thirdemissive surface configured to emit a third light, having a third amountof total luminance, in a third wavelength region of the EM spectrum. Thefirst, second, and third wavelength regions are different from eachother. The third luminance is greater than the first luminance and thesecond luminance. An area of the third emissive surface is smaller thanan area of the first emissive surface and an area of the second emissivesurface.

Further features and advantages of the invention, as well as thestructure and operation of various embodiments of the invention, aredescribed in detail below with reference to the accompanying drawings.It is noted that the invention is not limited to the specificembodiments described herein. Such embodiments are presented herein forillustrative purposes only. Additional embodiments will be apparent topersons skilled in the relevant art(s) based on the teachings containedherein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present embodiments and, togetherwith the description, further serve to explain the principles of thepresent embodiments and to enable a person skilled in the relevantart(s) to make and use the present embodiments.

FIG. 1 is a CIE 1976 u′v′ chromaticity diagram of Rec. 2020 color gamutand a color gamut of a display device.

FIGS. 2A, 2B, and 3 are exploded cross-sectional views of liquid crystaldisplay (LCD) devices, according to an embodiment.

FIG. 4 is an exploded cross-sectional view of an organic light emittingdiode (OLED) display device, according to an embodiment.

FIGS. 5A and 5B are exploded cross-sectional views of pixels of an OLEDdisplay device, according to an embodiment.

FIG. 6 is a schematic of a cross-sectional view of a nanostructure,according to an embodiment.

FIG. 7 is a schematic of a nanostructure film, according to anembodiment.

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The drawing in which an elementfirst appears is indicated by the leftmost digit(s) in the correspondingreference number. Unless otherwise indicated, the drawings providedthroughout the disclosure should not be interpreted as to-scaledrawings.

DETAILED DESCRIPTION OF THE INVENTION

Although specific configurations and arrangements may be discussed, itshould be understood that this is done for illustrative purposes only. Aperson skilled in the pertinent art will recognize that otherconfigurations and arrangements can be used without departing from thespirit and scope of the present invention. It will be apparent to aperson skilled in the pertinent art that this invention can also beemployed in a variety of other applications beyond those specificallymentioned herein. It should be appreciated that the particularimplementations shown and described herein are examples and are notintended to otherwise limit the scope of the application in any way.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” etc., indicate that theembodiment described may include a particular feature, structure, orcharacteristic, but every embodiment may not necessarily include theparticular feature, structure, or characteristic. Moreover, such phrasesdo not necessarily refer to the same embodiment. Further, when aparticular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of oneskilled in the art to effect such feature, structure or characteristicin connection with other embodiments whether or not explicitlydescribed.

All numbers in this description indicating amounts, ratios of materials,physical properties of materials, and/or use are to be understood asmodified by the word “about,” except as otherwise explicitly indicated.

In embodiments, the term “display device” refers to an arrangement ofelements that allow for the visible representation of data on a displayscreen. Suitable display screens may include various flat, curved orotherwise-shaped screens, films, sheets or other structures fordisplaying information visually to a user. Display devices describedherein may be included in, for example, display systems encompassing aliquid crystal display (LCD), televisions, computers, mobile phones,smart phones, personal digital assistants (PDAs), gaming devices,electronic reading devices, digital cameras, tablets, wearable devices,car navigation systems, and the like.

The term “about” as used herein indicates the value of a given quantityvaries by ±10% of the value. For example, “about 100 nm” encompasses arange of sizes from 90 nm to 110 nm, inclusive.

The term “substantially” as used herein indicates the value of a givenquantity varies by ±1% to ±5% of the value.

In embodiments, the term “forming a reaction mixture” or “forming amixture” refers to combining at least two components in a containerunder conditions suitable for the components to react with one anotherand form a third component.

In embodiment, the terms “light guide plate,” “light guide,” and “lightguide panel” are used interchangeably and refer to an optical componentthat is suitable for directing electromagnetic radiation (light) fromone position to another.

In embodiments, the term “optically coupled” means that components arepositioned such that light is able to pass from one component to anothercomponent without substantial interference.

The term “nanostructure” as used herein refers to a structure having atleast one region or characteristic dimension with a dimension of lessthan about 500 nm. In some embodiments, the nanostructure has adimension of less than about 200 nm, less than about 100 nm, less thanabout 50 nm, less than about 20 nm, or less than about 10 nm. Typically,the region or characteristic dimension will be along the smallest axisof the structure. Examples of such structures include nanowires,nanorods, nanotubes, branched nanostructures, nanotetrapods, tripods,bipods, nanocrystals, nanodots, QDs, nanoparticles, and the like.Nanostructures can be, e.g., substantially crystalline, substantiallymonocrystalline, polycrystalline, amorphous, or a combination thereof.In some embodiments, each of the three dimensions of the nanostructurehas a dimension of less than about 500 nm, less than about 200 nm, lessthan about 100 nm, less than about 50 nm, less than about 20 nm, or lessthan about 10 nm.

The term “QD” or “nanocrystal” as used herein refers to nanostructuresthat are substantially monocrystalline. A nanocrystal has at least oneregion or characteristic dimension with a dimension of less than about500 nm, and down to the order of less than about 1 nm. The terms“nanocrystal,” “QD,” “nanodot,” and “dot,” are readily understood by theordinarily skilled artisan to represent like structures and are usedherein interchangeably. The present invention also encompasses the useof polycrystalline or amorphous nanocrystals.

The term “heterostructure” when used with reference to nanostructuresrefers to nanostructures characterized by at least two different and/ordistinguishable material types. Typically, one region of thenanostructure comprises a first material type, while a second region ofthe nanostructure comprises a second material type. In certainembodiments, the nanostructure comprises a core of a first material andat least one shell of a second (or third etc.) material, where thedifferent material types are distributed radially about the long axis ofa nanowire, a long axis of an arm of a branched nanowire, or the centerof a nanocrystal, for example. A shell can but need not completely coverthe adjacent materials to be considered a shell or for the nanostructureto be considered a heterostructure; for example, a nanocrystalcharacterized by a core of one material covered with small islands of asecond material is a heterostructure. In other embodiments, thedifferent material types are distributed at different locations withinthe nanostructure; e.g., along the major (long) axis of a nanowire oralong a long axis of arm of a branched nanowire. Different regionswithin a heterostructure can comprise entirely different materials, orthe different regions can comprise a base material (e.g., silicon)having different dopants or different concentrations of the same dopant.

As used herein, the term “diameter” of a nanostructure refers to thediameter of a cross-section normal to a first axis of the nanostructure,where the first axis has the greatest difference in length with respectto the second and third axes (the second and third axes are the two axeswhose lengths most nearly equal each other). The first axis is notnecessarily the longest axis of the nanostructure; e.g., for adisk-shaped nanostructure, the cross-section would be a substantiallycircular cross-section normal to the short longitudinal axis of thedisk. Where the cross-section is not circular, the diameter is theaverage of the major and minor axes of that cross-section. For anelongated or high aspect ratio nanostructure, such as a nanowire, thediameter is measured across a cross-section perpendicular to the longestaxis of the nanowire. For a spherical nanostructure, the diameter ismeasured from one side to the other through the center of the sphere.

The terms “crystalline” or “substantially crystalline,” when used withrespect to nanostructures, refer to the fact that the nanostructurestypically exhibit long-range ordering across one or more dimensions ofthe structure. It will be understood by one of skill in the art that theterm “long range ordering” will depend on the absolute size of thespecific nanostructures, as ordering for a single crystal cannot extendbeyond the boundaries of the crystal. In this case, “long-rangeordering” will mean substantial order across at least the majority ofthe dimension of the nanostructure. In some instances, a nanostructurecan bear an oxide or other coating, or can be comprised of a core and atleast one shell. In such instances it will be appreciated that theoxide, shell(s), or other coating can but need not exhibit such ordering(e.g. it can be amorphous, polycrystalline, or otherwise). In suchinstances, the phrase “crystalline,” “substantially crystalline,”“substantially monocrystalline,” or “monocrystalline” refers to thecentral core of the nanostructure (excluding the coating layers orshells). The terms “crystalline” or “substantially crystalline” as usedherein are intended to also encompass structures comprising variousdefects, stacking faults, atomic substitutions, and the like, as long asthe structure exhibits substantial long range ordering (e.g., order overat least about 80% of the length of at least one axis of thenanostructure or its core). In addition, it will be appreciated that theinterface between a core and the outside of a nanostructure or between acore and an adjacent shell or between a shell and a second adjacentshell may contain non-crystalline regions and may even be amorphous.This does not prevent the nanostructure from being crystalline orsubstantially crystalline as defined herein.

The term “monocrystalline” when used with respect to a nanostructureindicates that the nanostructure is substantially crystalline andcomprises substantially a single crystal. When used with respect to ananostructure heterostructure comprising a core and one or more shells,“monocrystalline” indicates that the core is substantially crystallineand comprises substantially a single crystal.

The term “ligand” as used herein refers to a molecule capable ofinteracting (whether weakly or strongly) with one or more faces of ananostructure, e.g., through covalent, ionic, van der Waals, or othermolecular interactions with the surface of the nanostructure.

The term “quantum yield” (QY) as used herein refers to the ratio ofphotons emitted to photons absorbed, e.g., by a nanostructure orpopulation of nanostructures. As known in the art, quantum yield istypically determined by a comparative method using well-characterizedstandard samples with known quantum yield values.

The term “primary emission peak wavelength” as used herein refers to thewavelength at which the emission spectrum exhibits the highestintensity.

The term “full width at half-maximum” (FWHM) as used herein refers torefers to a measure of spectral width. In the case of an emissionspectrum, a FWHM can refer to a width of the emission spectrum at halfof a peak intensity value.

The term Forster radius used herein is also referred as Forster distancein the art.

The terms “luminance” and “brightness” are used herein interchangeablyand refer to a photometric measure of a luminous intensity per unit areaof a light source or an illuminated surface.

The term “radiance” as used herein refers to a radiometric measure of aradiant intensity per unit area of a light source or an illuminatedsurface.

The terms “specular reflectors,” “specularly reflective surfaces,” and“reflective surfaces” are used herein to refer to elements, materials,and/or surfaces capable of specular reflection.

The term “specular reflection” is used herein to refer to a mirror-likereflection of light (or of other kinds of wave) from a surface, when anincident light hits the surface.

The term “nanostructure (NS) film” is used herein to refer to a filmhaving luminescent nanostructures.

The term “red sub-pixel” is used herein to refer to an area of a pixelthat emits light having a primary emission peak wavelength in the redwavelength region of the visible spectrum. In some embodiments, the redwavelength region may include wavelengths ranging from about 620 nm toabout 750 nm.

The term “green sub-pixel” is used herein to refer to an area of a pixelthat emits light having a primary emission peak wavelength in the greenwavelength region of the visible spectrum. In some embodiments, thegreen wavelength region may include wavelengths ranging from about 495nm to about 570 nm.

The term “blue sub-pixel” is used herein to refer to an area of a pixelthat emits light having a primary emission peak wavelength in the bluewavelength region of the visible spectrum. In some embodiments, the bluewavelength region may include wavelengths ranging from about 435 nm toabout 495 nm.

The term “emissive surface of a sub-pixel” is used herein to refer to asurface of a topmost layer of the sub-pixel from which light is emittedtowards a display screen of a display device.

The term “luminance” is used herein to refer to a light intensity perunit area of an emissive surface.

The term “total luminance from a sub-pixel” is used herein to refer to alight intensity from per unit area of an emissive surface of thesub-pixel x total area of the emissive surface of the sub-pixel.

The published patents, patent applications, websites, company names, andscientific literature referred to herein are hereby incorporated byreference in their entirety to the same extent as if each wasspecifically and individually indicated to be incorporated by reference.Any conflict between any reference cited herein and the specificteachings of this specification shall be resolved in favor of thelatter. Likewise, any conflict between an art-understood definition of aword or phrase and a definition of the word or phrase as specificallytaught in this specification shall be resolved in favor of the latter.

Technical and scientific terms used herein have the meaning commonlyunderstood by one of skill in the art to which the present applicationpertains, unless otherwise defined. Reference is made herein to variousmethodologies and materials known to those of skill in the art.

Overview

This disclosure provides various embodiments of nanostructure-baseddisplay devices that help to improve or eliminate existing trade-offsbetween achieving the desired brightness and the desired color gamut indisplay devices. These various embodiments also help to improve displayperformance such as color gamut coverage of the nanostructure-baseddisplay devices by reducing or substantially eliminating leakage ofunwanted light through one or more pixels of the display devices.

Example Embodiments of a Liquid Crystal Display (LCD) Device

FIG. 2A illustrates a schematic of an exploded cross-sectional view ofan LCD display device 200, according to an embodiment. A person ofordinary skill in the art will recognize that the view of display devicein FIG. 2A is shown for illustration purposes and may not be drawn toscale. LCD display device 200 may include a backlight unit (BLU) 202 andan LCD module 204, according to an embodiment.

BLU 202 may include an optical cavity 212 and an array of LEDs 210(e.g., white LEDs, blue LEDs, UV LEDs, or a combination thereof) coupledto optical cavity 212. Optical cavity 212 may include a top side 203, abottom side 205, sidewalls 207, and a closed volume confined by top side203, bottom side 205, and sidewalls 207. LEDs 210 may be coupled to atop surface 205 a of bottom side 205 within the closed volume. LEDs 210may be configured to provide a primary light (e.g., a UV light, a bluelight, or a white light) that may be processed through LCD module 204and subsequently, transmitted to and distributed across a display screen230 of LCD display device 200. In some embodiments, LEDs 210 maycomprise blue LEDs that emit in the range from about 440 nm to about 470nm. In some embodiments, LEDs 210 may comprise white LEDs that emit inthe range from about 440 nm to about 700 nm or other possible lightwavelength ranges. In an embodiment, the array of LEDs 210 may comprisea two-dimensional array of LEDs that are spread across an area of topsurface 205 a and the area may be equal to the surface area of displayscreen 230.

It should be noted that even though two sidewalls 207 are shown in FIG.2A, a person skilled in the art would understand that optical cavity 212may include any number of sidewalls 207, according to variousembodiments. For example, optical cavity 212 may have a cuboid shape andmay include four sidewalls similar to sidewalls 207. Optical cavity 212is not restricted to being cuboid in shape or having otherstraight-sided shapes. Optical cavity 212 may be configured to be anytype of geometric shape, such as but not limited to cylindrical,trapezoidal, spherical, or elliptical, according to various embodiments,without departing from the spirit and scope of the present invention. Itshould also be noted that the rectangular cross-sectional shape ofoptical cavity 212, as illustrated in FIG. 2A, is for illustrativepurposes, and is not limiting. Optical cavity 212 may have othercross-sectional shapes (e.g., trapezoid, oblong, rhomboid), according tovarious embodiments, without departing from the spirit and scope of thepresent invention.

Top side 203 of optical cavity 212 may be configured to be an opticallydiffusive and transmissive layer such that light from LEDs 210 may exitoptical cavity 212 through top side 203 with a substantially uniformdistribution of brightness across top surface 203 a of top side 203. Inan embodiment, top side 203 may include optically transparent areas andoptically translucent areas that are strategically arranged over LEDs210 to provide the substantially uniform distribution in lightbrightness exiting top side 203. In another embodiment, top side 203 mayinclude pores of varying sizes in diameters and optically translucentareas that are strategically arranged to provide the substantiallyuniform distribution in light brightness exiting top side 203.

Bottom side 205 and/or sidewalls 207 may be constructed from one or morematerials (e.g., metals, non-metals, and/or alloys) that are configuredto have specularly reflective top surface 205 a and/or specularlyreflective side wall interior surfaces 207 a, respectively. For example,top surface 205 a and/or side wall interior surfaces 207 a may bemirror-like surfaces having mirror-like reflection properties. In someembodiments, top surface 205 a and/or side wall interior surfaces 207 amay be completely specularly reflective or partially specularlyreflective and partially scattering.

In alternate embodiments, optical cavity 212 may include specularreflectors 209 coupled to sidewall interior surfaces 207 a. Specularreflectors 209 may be coupled to sidewall interior surfaces 207 a usingoptically transparent adhesive. The optically transparent adhesive maycomprise tape, various glues, polymeric compositions such as silicones,etc. Additional optically transparent adhesive may include variouspolymers, including, but not limited to, poly(vinyl butyral), poly(vinylacetate), epoxies, and urethanes; silicone and derivatives of silicone,including, but not limited to, polyphenylmethylsiloxane,polyphenylalkylsiloxane, polydiphenylsiloxane, polydialkylsiloxane,fluorinated silicones and vinyl and hydride substituted silicones;acrylic polymers and copolymers formed from monomers including, but notlimited to, methylmethacrylate, butylmethacrylate, andlaurylmethacrylate; styrene based polymers; and polymers that are crosslinked with difunctional monomers, such as divinylbenzene, according tovarious examples.

Specularly reflective top surface 205 a and side wall interior surfaces207 a and specular reflectors 209 may substantially minimize absorptionof light from LEDs 210 through bottom side 205 and/or side walls 207 andthus, substantially minimize loss of luminance within optical cavity 212and increase light output efficiency of BLU 202.

In alternate embodiments, BLU 202 may further include one or morebrightness enhancement films (BEFs) (not shown) disposed between opticalcavity 212 and LCD module 204. The one or more BEFs may have reflectiveand/or refractive films, reflective polarizer films, light extractionfeatures, light recycling features, prism films, groove films, groovedprism films, prisms, pitches, grooves, or other suitable brightnessenhancement features. The brightness-enhancing features of BEFs may beconfigured to reflect a portion of the primary light (e.g., blue or UVlight from optical cavity 212) back toward optical cavity 212, therebyproviding recycling of the primary light.

LCD module 204 may be configured to process the light received from BLU202 to a desired characteristics for transmission to and distributionacross display screen 230. In some embodiments, LCD module 204 mayinclude one or more polarizing filters, such as first and secondpolarizing filters 214 and 222, one or more optically transparentsubstrates such as first and second optically transparent substrates 216and 228, switching devices 218.1 through 218.6 arranged in a 2-D arrayon first substrate 216, a liquid crystal (LC) solution layer 220, aplurality of pixels such as pixels 224.1 and 224.2 arranged in a 2-Darray, and display screen 230.

In some embodiments, pixel 224.1 may include sub-pixels 226.1 through226.3 and pixel 224.2 may include sub-pixels 226.4 through 226.6. Insome embodiments, each of pixels 224.1 and 224.2 may be tri-chromatic,for example, having red sub-pixels 226.1 and 226.4, green sub-pixels226.2 and 226.5, and blue sub-pixels 226.3 and 226.6, respectively.

The term “red sub-pixel” is used herein to refer to an area of a pixelthat emits light having a primary emission peak wavelength in the redwavelength region of the visible spectrum. In some embodiments, the redwavelength region may include wavelengths ranging from about 620 nm toabout 750 nm. The term “green sub-pixel” is used herein to refer to anarea of a pixel that emits light having a primary emission peakwavelength in the green wavelength region of the visible spectrum. Insome embodiments, the green wavelength region may include wavelengthsranging from about 495 nm to about 570 nm. The term “blue sub-pixel” isused herein to refer to an area of a pixel that emits light having aprimary emission peak wavelength in the blue wavelength region of thevisible spectrum. In some embodiments, the blue wavelength region mayinclude wavelengths ranging from about 435 nm to about 495 nm.

The arrangement order of red, green, and blue sub-pixels 226.1 through226.6 in respective pixels 224.1 and 224.2 is illustrative and is notlimiting. The red, green, and blue sub-pixels in each of pixels 224.1and 224.2 may be arranged in any order with respect to each other. Insome embodiments, pixels 224.1 and/or 224.2 may be monochromatic havingeither red, green, or blue sub-pixels 226.1 through 226.6. The number ofpixels and switching devices shown in FIG. 1 are illustrative and arenot limiting. LCD module 204 may have any number of switching devicesand pixels without departing from the spirit and scope of thisdisclosure.

Light from BLU 202 may be polarized through first polarizing filter 214and the polarized light may be transmitted to LC solution layer 220. LCsolution layer 220 may include LCs 232 having rod-shaped molecules thatmay act as shutters to control the amount of light transmission from LCsolution layer 220. In some embodiments, LCs 232 may be arranged in a3-D array. Columns 234.1 through 234.6 of the 3-D array of LCs may beindependently controlled by respective switching devices 218.1 through218.6. In some embodiments, switching devices 218.1 through 218.6 maycomprise transistors, such as, for example, thin film transistors(TFTs). By controlling LCs 232, the amount of light travelling fromcolumns 234.1 through 234.6 to respective sub-pixels 226.1 through 226.6may be controlled, and consequently, the amount of light transmittingfrom sub-pixels 226.1 through 226.6 is controlled.

LCs 232 may be twisted to varying degrees depending on the voltageapplied to columns 234.1 through 234.6 by respective switching devices218.1 through 218.6. By controlling the twisting of LCs 232, thepolarization angle of light passing through LC solution layer 220 may becontrolled. Light leaving LC solution layer 220 may then pass throughsecond polarizing filter 222 that may be positioned at 90 degrees withrespect to first polarizing filter 214. The angle of polarization of thelight leaving LC solution layer 220 and entering second polarizingfilter 222 may determine how much of the light is able to pass throughand exit from second polarizing filter 222. Second polarizing filter 222may attenuate the light, block the light, or allow the light to passwithout attenuation based on its angle of polarization.

Portions of light travelling through columns 234.1 through 234.6 of LCsand exiting out of second polarizing filter 222 may then enterrespective ones of sub-pixels 226.1 through 226.6. These portions oflight may undergo a stage of color filtering through the respective onesof sub-pixels 226.1 through 226.6 to achieve the desired opticalcharacteristics for light distribution across display screen 230. Insome embodiments, each of sub-pixels 226.1 through 226.6 may include aphosphor film 236 that may filter the portions of light enteringsub-pixels 226.1 through 226.6.

Phosphor films 236 may include luminescent nanostructures such as QDs(e.g., QD 600 described with reference to FIG. 6), according to someembodiments. Phosphor films 236 may be down-converters, where theportions of light (also referred as primary light) entering therespective ones of sub-pixels 226.1 through 226.6 may be absorbed, forexample, by the luminescent nanostructures in phosphor films 236 andre-emitted as secondary light having a lower energy or longer wavelengththan the primary light.

In some embodiments, phosphor films 236 of red sub-pixels 226.1 and226.4 may include luminescent nanostructures that absorb the primarylight and emit a first secondary light having a primary emission peakwavelength in the red wavelength region of the visible spectrum light.In some embodiments, phosphor films 236 of green sub-pixels 226.2 and226.5 may include luminescent nanostructures that absorb the primarylight and emit a second secondary light having a primary emission peakwavelength in the green wavelength region of the visible spectrum light.

In some embodiments, when BLU 202 has UV LEDs 210, phosphor films 236 ofblue sub-pixels 226.3 and 226.6 may include luminescent nanostructuresthat absorb the primary light and emit a third secondary light having aprimary emission peak wavelength in the blue wavelength region of thevisible spectrum light.

In some embodiments, phosphor films 236 may be segmented films that areplaced adjacent to each other on second polarizing filter 222 or on anoptically transparent substrate (not shown). The segmented phosphorfilms 236 may be placed in a manner such that there is negligible gap atinterfaces between adjacent phosphor films 236 to prevent leakage ofprimary light through the interfaces. In alternate embodiments, each ofphosphor films 236 may be different regions of a continuous phosphorfilm.

Additionally, each of sub-pixels 226.1 through 226.6 may include a lightblocking element 238 disposed on phosphor film 236, according to someembodiments. The secondary light emitting from phosphor films 236 may befiltered through corresponding ones of light blocking elements 238before travelling to display screen 230.

Light blocking elements 238 may be configured to allow the secondarylight (e.g., first, second, and/or third secondary light discussedabove) to pass and to block portions of the primary light (e.g., bluelight or UV light) that are not absorbed by phosphor films 236 anddown-converted to the secondary light. The unwanted portions of primarylight that may have leaked out of phosphor films 236 may be blocked byabsorbing and/or scattering them. Leakage of the unconverted primarylight from phosphor films 236 to display screen 230 may adversely affectthe color gamut coverage of LCD display device 200. The use of lightblocking elements 238 to prevent such leakage may also help to reducethe manufacturing cost of LCD display device 200 by reducing the densityof luminescent nanostructures included in phosphor films 236. Thedensity of luminescent nanostructures may be reduced as instead of usingthe luminescent nanostructures to absorb substantially all portions ofthe primary light, any portions of primary light not absorbed inphosphor films 236 may be filtered out by light blocking elements 238.

Light blocking elements 238 may be also configured to tune the spectralemission widths (also referred as width of emission spectrum) of thesecondary light (e.g., first, second, and/or third secondary lightdiscussed above) to achieve a desired color gamut coverage of LCDdisplay device 200. Tuning of the spectral emission widths may requireabsorbing one or more wavelengths from the secondary light to narrowtheir spectral emission widths to achieve the desired color gamutcoverage without significant decrease in brightness. For example, theremay be less than 10% (e.g., about 8%, about 5%, about 3%, or about 1%)decrease in brightness due to this tuning process compared to displaydevices without light blocking elements 238. As the secondary light fromphosphor films 236 having luminescent nanostructures such as QDstypically exhibit narrow spectral emission widths, the tuning processmay not require absorption of wide range of wavelengths to achieve thedesired color gamut coverage as required in current non-QD based displaydevices to achieve similar color gamut coverage.

Wide spectral emission width is one of the limitations in current non-QDbased display devices (e.g., YAG-phosphor based display devices) inachieving wide color gamut coverage of, for example, the Rec. 2020 colorspace. Use of absorbing elements such as light blocking elements 238 incurrent non-QD based display devices may achieve wide color gamutcoverage (e.g., 80-90% Rec. 2020 color gamut coverage), but at the costof significant decrease in brightness. Such decrease in brightness maynot only adversely affect the image quality of the current displaydevices, but also fail to meet the brightness level required under theHDR imaging standards.

Light blocking elements 238 may include one or more non-phosphormaterials. That is, the one or more non-phosphor materials exhibitoptical absorption properties and/or optical scattering properties, butdo not exhibit optical emission properties. The one or more non-phosphormaterials may be selected based on their optical absorption propertiesto absorb and/or on their scattering properties to scatter only the oneor more wavelengths or range of wavelengths that require absorbingand/or scattering during the above described blocking and tuningprocesses. In some embodiments, the one or more non-phosphor materialsmay include the same absorption property. In some embodiment, each ofthe one or more non-phosphor materials includes an absorption propertydifferent from each other.

The one or more non-phosphor materials may be selected such that theymay be inexpensively disposed on phosphor films 236 or any otherlayer/structure of LCD display device 200 to form light blockingelements 238. For example, the one or more non-phosphor materials may bedye (e.g., narrow band organic Exciton P491 dye), ink, paint, polymericmaterial, an/or any material that may be sprayed, painted, spin-coated,printed, or any other suitable low temperature (e.g., below 100° C.)deposition method. Printing may be done using, for example, a plotter,an inkjet printer, or a screen printer. In some embodiments, the one ormore non-phosphor materials may be directly disposed on phosphor films238. In some embodiments, the one or more non-phosphor materials may bescattering materials that include films or particles (e.g., particleshaving diameters ranging from about 100 nm to about 500 μm) of titaniumoxide, zinc oxide, zinc sulfide, silicone, or a combination thereof. Insome embodiments, light blocking elements 238 may include a substratehaving the one or more non-phosphor materials disposed on it.

In some embodiments, light blocking elements 238 may be segmented filmsthat are placed adjacent to each other on phosphor films 236 or on anoptically transparent substrate (not shown). The segmented lightblocking elements 238 may be placed in a manner such that there isnegligible gap at interfaces between adjacent light blocking elements238. In alternate embodiments, each of light blocking elements 238 maybe different regions of a continuous film placed on phosphor films 236.Thus, FIG. 2A is not depicted to scale.

In some embodiments, light blocking elements 238 may not be a separatestructure as shown in FIG. 2A, but may be included in phosphor films236. That is, phosphor films 236 may be a composite film comprising theluminescent nanostructures, as described above, along with lightblocking elements 238. The one or more non-phosphor materials of lightblocking elements 238 such as dye, ink, paint, polymeric material,scattering materials (e.g., particles having diameters ranging fromabout 100 nm to about 500 μm), or a combination thereof may beincorporated or embedded in a matrix of phosphor films 236. The one ormore non-phosphor materials may include nanostructured materials thatmay be dispersed in a matrix of phosphor films 236. These nanostructuredmaterials may exhibit optical absorption properties and/or opticalscattering properties and may not exhibit any optical emissionproperties. In some embodiments, light blocking elements 238 may beincluded in optically transparent substrate 228, which may also beconfigured to provide environmental sealing to the underlying layersand/or structures of LCD module 204 and/or BLU 202. In alternateembodiments, light blocking elements 238 may be included in secondpolarizing filter 222, which may be positioned between substrate 228 andphosphor films 236.

Display screen 230 may be configured to generate images. Display screen230 may be a touch screen display, according to an embodiment. LCDdisplay device 200 may further include one or more medium materials (notshown) disposed between any of the adjacent elements in LCD displaydevice 200, for example between optical cavity 212 and LCD module 204,on either sides of LC solution layer 220, or between any other elementsof LCD display device 200. The one or more medium materials may include,but not limited to, substrates, a vacuum, air, gas, optical materials,adhesives, optical adhesives, glass, polymers, solids, liquids, gels,cured materials, optical coupling materials, index-matching orindex-mismatching materials, index-gradient materials, cladding oranti-cladding materials, spacers, epoxy, silica gel, silicones,brightness-enhancing materials, scattering or diffuser materials,reflective or anti-reflective materials, wavelength-selective materials,wavelength-selective anti-reflective materials, or other suitable mediummaterial. Suitable materials may include silicones, silicone gels,silica gel, epoxies (e.g., Loctite™ Epoxy E-30CL), acrylates (e.g., 3M™Adhesive 2175). The one or more medium materials may be applied as acurable gel or liquid and cured during or after deposition, orpre-formed and pre-cured prior to deposition. Curing methods may includeUV curing, thermal curing, chemical curing, or other suitable curingmethods known in the art. Index-matching medium materials may be chosento minimize optical losses between elements of BLU 202 and LCD module204.

LCD display device 200 may have a geometric shape, such as but notlimited to cylindrical, trapezoidal, spherical, or elliptical, accordingto various embodiments, without departing from the spirit and scope ofthe present invention. LCD display device 200 is not restricted to beingcuboid in shape or having other straight-sided shapes. It should benoted that the rectangular cross-sectional shape of LCD display device200 is for illustrative purposes, and is not limiting. LCD displaydevice 200 may have other cross-sectional shapes (e.g., trapezoid,oblong, rhomboid), according to various embodiments, without departingfrom the spirit and scope of the present invention. It should also benoted that even though optical cavity 212, substrates 216 and 228,polarizing filter 214 and 222, and display screen 230 are shown in FIG.2A to have similar dimensions along X-axis, a person skilled in the artwould understand that each of these components may have dimensionsdifferent from each other in one or more directions, according tovarious embodiments.

FIG. 2B illustrates an LCD display device 200*, which is an alternateembodiment of LCD display device 200. LCD display device 200* mayinclude LEDs 210 having blue LEDs. LCD display device 200* may furtherinclude blue sub-pixels 226.3* and 226.6* that have film elements 236*and 238* instead of phosphor films 236 and light blocking elements 238described above. Film elements 236* and 238* may exclude luminescentnanostructures such as QDs and may be optically transparent to bluelight from blue LEDs 210. Such exclusion and transparency may bepossible because down-conversion of primary blue light from blue LEDs210 and/or blocking of blue light may not be needed for blue sub-pixels226.3* and 226.6*. In some embodiments, film elements 236* and 238*include scattering components to scatter the blue light from blue LEDs210, such that the angular distribution of light from blue sub-pixels226.3* and 226.6* matches that from the green sub-pixels 226.2 and226.5, and red sub-pixels 226.1 and 226.4.

The above discussion of display device 200, LCD module 204, pixels 224.1and 224.2, and sub-pixels 226.3 and 226.6 applies to display device200*, LCD module 204*, pixels 224.1* and 224.2*, and sub-pixels 226.3*and 226.6, unless mentioned otherwise. Elements in FIG. 2B with the sameannotations as elements in FIG. 2A are described above. Sub-pixels226.1, 226.2, and 226.3* may be similar in structure, composition, andfunction to respective sub-pixels 226.4, 226,5, and 226.6*, according tosome embodiments. The description of sub-pixels 226.1, 226,2, and 226.3*applies to sub-pixels 226.4, 226,5, and 226.6*, respectively, unlessmentioned otherwise.

In some embodiments, sub-pixels 226.1, 226.2, and 226.3* may haveemissive surfaces along a plane (e.g., XY plane) that may besubstantially parallel to a plane of display screen 230 along whichlight from these sub-pixels are distributed. The term “emissive surfaceof a sub-pixel” is used herein to refer to a surface of a topmost layerof the sub-pixel from which light is emitted towards a display screen ofa display device.

In some embodiments, top surfaces 238.1 s, 238.2 s, and 238.3 s* oflight blocking elements 238 and film 238* may form the emissive surfacesof sub-pixels 226.1, 226.2, and 226.3*, respectively. Similarly, topsurfaces 238.4 s, 238.5 s, 238.6 s* may form the emissive surfaces ofsub-pixels 226.4, 226.5, and 226.6*, respectively.

In alternate embodiments, sub-pixels 226.1, 226.2, 226.3*, 226.4, 226.5,and 226.6* may exclude light blocking elements 238 and film 238*, andmay have phosphor films 236 and film elements 236* as the topmost layersin these sub-pixels. In this embodiment, top surfaces 236.1 s, 236.2 s,236.3 s*, 236.4 s, 236.5 s, and 236.6 s* may form the emissive surfacesof these sub-pixels.

In some embodiments, areas of the emissive surfaces (also referred asemissive surface areas) of sub-pixels 226.1, 226.2, and 226.3* are suchthat the total light emitted from each of sub-pixels 226.1, 226.2, and226.3* produces a desired white point. For example, the emissive surfacearea of each of sub-pixels 226.1, 226.2, and 226.3* may be chosen suchthat the total luminance from each of red, green, and blue sub-pixels226.1, 226.2, and 226.3*, respectively, achieves the desired white pointvalue and brightness on display screen 230 required by high dynamicrange (HDR) imaging standards.

The relative areas of the emissive surfaces of sub-pixels 226.1, 226.2,and 226.3* may be based on the relative luminance of the red, green, andblue lights emitted from sub-pixels 226.1, 226.2, and 226.3*,respectively. The term “luminance” is used herein to refer to a lightintensity per unit area of an emissive surface. The relative luminanceof these red, green, and blue lights may depend on the down-conversionefficiency of luminescent nanostructures such as QDs (e.g., QDs 600 ofFIG. 6) in phosphor films 236 of red and green sub-pixels 226.1 and226.2 and on the luminance of blue light from blue LEDs 210.

In an example where the emissive surface area of each of sub-pixels226.1, 226.2, and 226.3* is substantially the same, the luminance of theprimary blue light from blue LEDs 210 may be stronger than the luminanceof the red and/or green light emitted from red and green sub-pixels226.1 and 226.2. This higher luminance of the blue light may be becausethe blue light from sub-pixel 226.3* is the primary blue light from blueLEDs 210, and not from down-conversion of the primary blue light.Down-conversion of a primary light may lose some of the luminance of theprimary light as in the case of the emitted red and/or green lights,which result from down-conversion of the primary blue light inrespective sub-pixels 226.1 and 226.2. Hence, the relative areas of theemissive surfaces of sub-pixels 226.1, 226.2, and 226.3* may depend onthe down-conversion efficiency of the luminescent nanostructures inphosphor films 236 of red and green sub-pixels 226.1 and 226.2 and onthe luminance of the primary blue light from blue LEDs 210.

In some embodiments, the emissive surface area of blue sub-pixel 226.3*may be smaller than emissive surface areas of red sub-pixel 226.1 and/orgreen sub-pixel 226.2. In some embodiments, a first ratio between theemissive surface areas of sub-pixels 226.1, 226.2, and 226.3* and asecond ratio between the emissive surface areas of sub-pixels 226.4226.5, and 226.6* may each range from about 2:2:1 to about 6:6:1 (e.g.,about 2:3:1, about 3:2:1, about 3:3:1, about 4:3:1, about 3:4;1, about4:4:1, about 5:4:1, about 4:5:1, about 5:5:1, about 6:5:1, about 5:6:1,or about 6:6:1). Such dimensions of sub-pixels 226.1, 226,2, and 226.3*may achieve over 60% (e.g., about 70%, about 80%, or about 90%) increasein brightness in LCD display device 200* for a white point valuecompared to LCD display devices having equal sized red, green, and bluesub-pixels per pixel.

In some embodiments, the combined emissive surface areas of sub-pixels226.1, 226.2, and 226.3* may form the emissive surface area of pixel224.1 and the combined emissive surface areas of sub-pixels 226.4,226.5, and 226.6* may form the emissive surface area of pixel 224.2. Insome embodiments, emissive surface areas of pixels 224.1* and 224.2* maybe substantially equal to each other, even though the respective firstand second ratios are different from each other.

Based on the disclosure herein, a person of ordinary skill in the artwill recognize that other ratios for the first and second ratios arewithin the scope and spirit of this disclosure.

FIG. 3 illustrates a schematic of an exploded cross-sectional view of anedge-lit LCD display device 300, according to an embodiment. LCD displaydevice 300 may include a BLU 302 and LCD module 204. Elements in FIG. 3with the same annotations as elements in FIG. 2A are described above.

BLU 302 may include an LED 310 (e.g., a blue LED or a UV LED), a lightguide plate (LGP) 312, and a reflector 308. BLU 302 may be configured toprovide a primary light (e.g., a blue light or a UV light) that may beprocessed through LCD module 204 and subsequently, transmitted to anddistributed across display screen 230. The blue LED may emit in therange from about 440 nm to about 470 nm. According to an embodiment, theblue LED may be, for example, a GaN LED that emits blue light at awavelength of 450 nm.

LGP 312 may include fiber optic cables, polymeric or glass solid bodiessuch as plates, films, containers, or other structures, according tosome embodiments. The size of LGP 312 may depend on the ultimateapplication and characteristics of LED 310. The thickness of LGP 312 maybe compatible with thickness of LED 310. The other dimensions of LGP 312may be designed to extend beyond the dimensions of LED 310, and may beon the order of 10's of millimeters, to 10's to 100's of centimeters.

In some embodiments, the materials of LGP 312 may include polycarbonate(PC), poly methyl methacrylate (PMMA), methyl methacrylate, styrene,acrylic polymer resin, glass, or other suitable LGP materials. Suitablemanufacturing methods for LGP 312 may include injection molding,extrusion, or other suitable embodiments. LGP 312 may be configured toprovide uniform primary light emission, such that primary light enteringLCD module 204 may be of uniform color and brightness. LGP 312 mayinclude a substantially uniform thickness over the entire LGP 512surface. Alternatively, LGP 312 may have a wedge-like shape. In someembodiments, LGP 312 may be optically coupled to LED 310 and may bephysically connected to or detached from LED 310. For physicallyconnecting LGP 312 to LED 310, optically transparent adhesive may beused (not shown).

In some embodiments, BLU 302 may include an array of LEDs (not shown),each of which may be similar to LED 310 in structure and function. Thearray of LEDs may be adjacent to LGP 312 and may be configured toprovide the primary light to LCD module 204 for processing and forsubsequent transmission to display screen 230 as discussed above withreference to FIG. 2A.

In some embodiments, reflector 308 may be configured to increase theamount of light that is emitted from LGP 512. Reflector 308 may comprisea suitable material, such as a reflective mirror, a film of reflectorparticles, a reflective metal film, or other suitable conventionalreflectors. In some embodiments, reflector 308 may include a white film.In some embodiments, reflector 308 may include additional functionalityor features, such as scattering, diffuser, or brightness-enhancingfeatures.

In alternate embodiments, LCD display device 300 may have LCD module204* as shown in FIG. 2B instead of LCD module 204 as shown in FIG. 2A.

Example Embodiments of an Organic Light Emitting Diode (OLED) DisplayDevice

FIG. 4 illustrates a schematic of an exploded cross-sectional view of anorganic light emitting diode (OLED) display device 400, according to anembodiment. OLED display device 400 may include a back plate 418, aplurality of pixels 424 arranged in a 2-D array on back plate 418, and atransmissive cover plate 430, according to an embodiment. The number ofpixels shown in FIG. 4 is illustrative and is not limiting. OLED displaydevice 400 may have any number pixels without departing from the spiritand scope of this disclosure.

Cover plate 430 may serve as display screen to generate images and/ormay be configured to provide environmental sealing to underlyingstructures of OLED display device 400. Cover plate 430 may be alsoconfigured to be an optically transparent substrate on which othercomponents (e.g., electrode) of OLED display device 400 may be disposed.In some embodiments, pixels 424 may be tri-chromatic having red, green,and blue sub-pixels. In some embodiments, pixels 424 may bemonochromatic having either red, green, or blue sub-pixels. In someembodiments, OLED display device 400 may have a combination of bothtri-chromatic and monochromatic pixels 424.

OLED display device 400 may further include control circuitry (notshown) of pixels 424. Pixels 424 may be independently controlled byswitching devices such as, for example, thin film transistors (TFTs).OLED display device 400 may have a geometric shape, such as but notlimited to cylindrical, trapezoidal, spherical, or elliptical, accordingto various embodiments, without departing from the spirit and scope ofthe present invention. It should be noted that even though back plate418, array of pixels 424, and cover plate 430 are shown in FIG. 4 tohave similar dimensions along X-axis, a person skilled in the art wouldunderstand that each of these components may have dimensions differentfrom each other in one or more directions, according to variousembodiments.

FIG. 5A illustrates an exploded cross-sectional view of a tri-chromaticpixel 524 of an OLED display device, according to an embodiment. One ormore of pixels 424 of OLED display device 400 of FIG. 4 may have aconfiguration similar to pixel 524. Pixel 524 may include a redsub-pixel 540, a green sub-pixel 542, and a blue sub-pixel 544. Thearrangement order of red, green, and blue sub-pixels 540, 542, and 544is illustrative and is not limiting. The red, green, and blue sub-pixels540, 542, and 544 may be arranged in any order with respect to eachother.

Each of red, green, and blue sub-pixels 540, 542, and 544 may include alight source 546 (e.g., a blue OLED or a UV OLED) and a light blockingelement 548. The above discussion of light blocking elements 238 appliesto light blocking elements 548 unless mentioned otherwise.

Red sub-pixel 540 may further include a phosphor film 550 disposed on anemitting surface of light source 546 of red sub-pixel 540. Phosphor film550 may have luminescent nanostructures such as QDs (e.g., QD 600described with reference to FIG. 6) that absorb primary light from lightsource 546 of red sub-pixel 540 and emit red light having a primaryemission peak wavelength in the red wavelength region of the visiblespectrum.

Green sub-pixel 542 may further include a phosphor film 552 disposed onan emitting surface of light source 546 of green sub-pixel 542. Phosphorfilm 552 may have luminescent nanostructures such as QDs (e.g., QD 600described with reference to FIG. 6) that absorb primary light from lightsource 546 of green sub-pixel 542 and emit green light having a primaryemission peak wavelength in the green wavelength region of the visiblespectrum.

Blue sub-pixel 544 may further include a phosphor film 554 disposed onan emitting surface of light source 546 of blue sub-pixel 544 when lightsource 546 has a UV OLED, according to an embodiment. Phosphor film 554may have luminescent nanostructures such as QDs (e.g., QD 600 describedwith reference to FIG. 6) that absorb primary light from the UV OLED andemit blue light having a primary emission peak wavelength in the bluewavelength region of the visible spectrum.

Light blocking elements 548 may be configured to filter the red, green,and blue lights emitted from respective phosphor films 550, 552, and 554before travelling to a cover plate such as cover plate 430 of FIG. 4.Light blocking elements 548 may be configured to allow the red, green,and blue lights from respective phosphor films 550, 552, and 554 to passand to block portions of primary light from light source 546 that arenot absorbed by phosphor films 550, 552, and 554, and down-converted tothe red, green, and blue light, respectively. The unwanted portions ofthe primary light that may have leaked out of phosphor films 550, 552,and 554 may be blocked by absorbing and/or scattering them. Lightblocking elements 548 may be also configured to tune the spectralemission widths (also referred as width of emission spectrum) of thered, green, and blue light emitted from respective phosphor films 550,552, and 554 to achieve a desired color gamut coverage of OLED displaydevice 400.

In some embodiments, light blocking elements 548 may not be a separatestructure as shown in FIG. 5A, but may be included in phosphor films550, 552, and 554. That is, phosphor films 550, 552, and 554 may becomposite films comprising the luminescent nanostructures, as describedabove, along with light blocking elements 548. The one or morenon-phosphor materials of light blocking elements 548 such as dye, ink,paint, polymeric material, scattering materials (e.g., particles havingdiameters ranging from about 100 nm to about 500 μm), or a combinationthereof may be incorporated or embedded in matrices of phosphor films550, 552, and 554. The one or more non-phosphor materials may includenanostructured materials that may be dispersed in matrices of phosphorfilms 550, 552, and 554. These nanostructured materials may exhibitoptical absorption properties and/or optical scattering properties andmay not exhibit any optical emission properties.

FIG. 5B illustrates a pixel 524*, which is an alternate embodiment ofOLED based pixel 524 shown in FIG. 5A. Pixel 524* may include lightsource 546 having a blue OLED. Pixel 524* may further include opticallytransparent films 554* and 548* instead of phosphor film 554 and lightblocking element 548 described above. The optically transparent films554* and 548* may exclude luminescent nanostructures such as QDs and maybe optically transparent to blue light from blue OLED 546. Suchexclusion and transparency may be possible because down-conversion ofprimary blue light from blue OLED 546 and/or blocking of blue light maynot be needed for blue sub-pixel 544*.

The above discussion of blue sub-pixel 544 applies to blue sub-pixel544*, unless mentioned otherwise. Elements in FIG. 5B with the sameannotations as elements in FIG. 5A are described above.

In some embodiments, sub-pixels 540, 542, and 544* may have emissivesurfaces along a plane (e.g., XY plane) that may be substantiallyparallel to a plane of display screen (e.g., display screen 430) alongwhich light from these sub-pixels are distributed. In some embodiments,top surfaces 540 s, 542 s, and 548* of light blocking elements 548 andfilm 548* may form the emissive surfaces of sub-pixels 540, 542, and544*, respectively.

In alternate embodiments, sub-pixels 540, 542, and 544* may excludelight blocking elements 548 and film 548*, and may have phosphor films550 and 552 and film 554* as the topmost layers in these sub-pixels. Inthis embodiment, top surfaces 550 s, 552 s, and 554* may form theemissive surfaces of these sub-pixels.

In some embodiments, areas of the emissive surfaces of sub-pixels 540,542, and 544* are such that the total luminance emitted from each ofsub-pixels 540, 542, and 544* produces a desired white point. Therelative areas of these emissive surfaces may be based on the relativeluminance of the red, green, and blue lights emitted from sub-pixels540, 542, and 544*, respectively. The relative luminance of these red,green, and blue lights may depend on the down-conversion efficiency ofluminescent nanostructures such as QDs (e.g., QDs 600 of FIG. 6) inphosphor films 550 and 552 of respective red and green sub-pixels 540and 542 and on the luminance of blue light from blue OLED 546. Hence,the relative areas of the emissive surfaces of sub-pixels 540, 542, and544* may depend on the down-conversion efficiency of the luminescentnanostructures of red and green sub-pixels 540 and 542 and on theluminance of the primary blue light from blue OLED 546.

In some embodiments, emissive surface area of blue sub-pixel 544* may besmaller than emissive surface areas of red sub-pixel 542 and/or greensub-pixel 542. In some embodiments, a ratio between the emissive surfaceareas of sub-pixels 540, 542, and 544* may range from about 3:3:1 toabout 6:6:1 (e.g., about 4:3:1, about 3:4;1, about 4:4:1, about 5:4:1,about 4:5:1, about 5:5:1, about 6:5:1, about 5:6:1, or 6:6:1).

In some embodiments, the combined emissive surface areas of sub-pixels540, 542, and 544* may form the emissive surface area of pixel 524*. Insome embodiments, emissive surface areas of adjacent pixels (e.g., apair of pixel 524*) may be substantially equal to each other, eventhough the ratios between the emissive surface areas of sub-pixelsincluded in respective one of the adjacent pixels are different fromeach other.

Example Embodiments of a Barrier Layer Coated Nanostructure

FIG. 6 illustrates a cross-sectional structure of a barrier layer coatedluminescent nanostructure (NS) 600, according to an embodiment. In someembodiments, a population of NS 600 may be included in phosphor films236, 550, 552, and/or 554. Barrier layer coated NS 600 includes a NS 601and a barrier layer 606. NS 601 includes a core 602 and a shell 604.Core 602 includes a semiconducting material that emits light uponabsorption of higher energies. Examples of the semiconducting materialfor core 602 include indium phosphide (InP), cadmium selenide (CdSe),zinc sulfide (ZnS), lead sulfide (PbS), indium arsenide (InAs), indiumgallium phosphide, (InGaP), cadmium zinc selenide (CdZnSe), zincselenide (ZnSe) and cadmium telluride (CdTe). Any other II-VI, III-V,tertiary, or quaternary semiconductor structures that exhibit a directband gap may be used as well. In an embodiment, core 602 may alsoinclude one or more dopants such as metals, alloys, to provide someexamples. Examples of metal dopant may include, but not limited to, zinc(Zn), Copper (Cu), aluminum (Al), platinum (Pt), chrome (Cr), tungsten(W), palladium (Pd), or a combination thereof. The presence of one ormore dopants in core 602 may improve structural and optical stabilityand QY of NS 601 compared to undoped NSs.

Core 602 may have a size of less than 20 nm in diameter, according to anembodiment. In another embodiment, core 602 may have a size betweenabout 1 nm and about 5 nm in diameter. The ability to tailor the size ofcore 602, and consequently the size of NS 601 in the nanometer rangeenables photoemission coverage in the entire optical spectrum. Ingeneral, the larger NSs emit light towards the red end of the spectrum,while smaller NSs emit light towards the blue end of the spectrum. Thiseffect arises as larger NSs have energy levels that are more closelyspaced than the smaller NSs. This allows the NS to absorb photonscontaining less energy, i.e. those closer to the red end of thespectrum.

Shell 604 surrounds core 602 and is disposed on outer surface of core602. Shell 604 may include cadmium sulfide (CdS), zinc cadmium sulfide(ZnCdS), zinc selenide sulfide (ZnSeS), and zinc sulfide (ZnS). In anembodiment, shell 604 may have a thickness 604 t, for example, one ormore monolayers. In other embodiments, shell 604 may have a thickness604 t between about 1 nm and about 5 nm. Shell 604 may be utilized tohelp reduce the lattice mismatch with core 602 and improve the QY of NS601. Shell 604 may also help to passivate and remove surface trapstates, such as dangling bonds, on core 602 to increase QY of NS 601.The presence of surface trap states may provide non-radiativerecombination centers and contribute to lowered emission efficiency ofNS 601.

In alternate embodiments, NS 601 may include a second shell disposed onshell 604, or more than two shells surrounding core 602, withoutdeparting from the spirit and scope of the present invention. In anembodiment, the second shell may be on the order of two monolayers thickand is typically, though not required, also a semiconducting material.Second shell may provide protection to core 602. Second shell materialmay be zinc sulfide (ZnS), although other materials may be used as wellwithout deviating from the scope or spirit of the invention.

Barrier layer 606 is configured to form a coating on NS 601. In anembodiment, barrier layer 606 is disposed on and in substantial contactwith outer surface 604 a of shell 604. In embodiments of NS 601 havingone or more shells, barrier layer 606 may be disposed on and insubstantial contact with the outermost shell of NS 601. In an exampleembodiment, barrier layer 606 is configured to act as a spacer betweenNS 601 and one or more NSs in, for example, a solution, a composition,and/or a film having a plurality of NSs, where the plurality of NSs maybe similar to NS 601 and/or barrier layer coated NS 600. In such NSsolutions, NS compositions, and/or NS films, barrier layer 606 may helpto prevent aggregation of NS 601 with adjacent NSs. Aggregation of NS601 with adjacent NSs may lead to increase in size of NS 601 andconsequent reduction or quenching in the optical emission properties ofthe aggregated NS (not shown) including NS 601. In further embodiments,barrier layer 606 provides protection to NS 601 from, for example,moisture, air, and/or harsh environments (e.g., high temperatures andchemicals used during lithographic processing of NSs and/or duringmanufacturing process of NS based devices) that may adversely affect thestructural and optical properties of NS 601.

Barrier layer 606 includes one or more materials that are amorphous,optically transparent and/or electrically inactive. Suitable barrierlayers include inorganic materials, such as, but not limited to,inorganic oxides and/or nitrides. Examples of materials for barrierlayer 606 include oxides and/or nitrides of Al, Ba, Ca, Mg, Ni, Si, Ti,or Zr, according to various embodiments. Barrier layer 606 may have athickness 606 t ranging from about 8 nm to about 15 nm in variousembodiments.

As illustrated in FIG. 6, barrier layer coated NS 600 may additionallyor optionally include a plurality of ligands or surfactants 608,according to an embodiment. Ligands or surfactants 608 may be adsorbedor bound to an outer surface of barrier layer coated NS 600, such as onan outer surface of barrier layer 606, according to an embodiment. Theplurality of ligands or surfactants 608 may include hydrophilic or polarheads 608 a and hydrophobic or non-polar tails 608 b. The hydrophilic orpolar heads 608 a may be bound to barrier layer 606. The presence ofligands or surfactants 608 may help to separate NS 600 and/or NS 601from other NSs in, for example, a solution, a composition, and/or a filmduring their formation. If the NSs are allowed to aggregate during theirformation, the quantum efficiency of NSs such as NS 600 and/or NS 601may drop. Ligands or surfactants 608 may also be used to impart certainproperties to barrier layer coated NS 600, such as hydrophobicity toprovide miscibility in non-polar solvents, or to provide reaction sites(e.g., reverse micellar systems) for other compounds to bind.

A wide variety of ligands exist that may be used as ligands 608. In someembodiments, the ligand is a fatty acid selected from lauric acid,caproic acid, myristic acid, palmitic acid, stearic acid, and oleicacid. In some embodiments, the ligand is an organic phosphine or anorganic phosphine oxide selected from trioctylphosphine oxide (TOPO),trioctylphosphine (TOP), diphenylphosphine (DPP), triphenylphosphineoxide, and tributylphosphine oxide. In some embodiments, the ligand isan amine selected from dodecylamine, oleylamine, hexadecylamine, andoctadecylamine. In some embodiments, the ligand is trioctylphosphine(TOP). In some embodiments, the ligand is oleylamine. In someembodiments, the ligand is diphenylphosphine.

A wide variety of surfactants exist that may be used as surfactants 608.Nonionic surfactants may be used as surfactants 608 in some embodiments.Some examples of nonionic surfactants include polyoxyethylene (5)nonylphenylether (commercial name IGEPAL CO-520), polyoxyethylene (9)nonylphenylether (IGEPAL CO-630), octylphenoxy poly(ethyleneoxy)ethanol(IGEPAL CA-630), polyethylene glycol oleyl ether (Brij 93), polyethyleneglycol hexadecyl ether (Brij 52), polyethylene glycol octadecyl ether(Brij S10), polyoxyethylene (10) isooctylcyclohexyl ether (TritonX-100), and polyoxyethylene branched nonylcyclohexyl ether (TritonN-101).

Anionic surfactants may be used as surfactants 608 in some embodiments.Some examples of anionic surfactants include sodium dioctylsulfosuccinate, sodium stearate, sodium lauryl sulfate, sodiummonododecyl phosphate, sodium dodecylbenzenesulfonate, and sodiummyristyl sulfate.

In some embodiments, NSs 601 and/or 600 may be synthesized to emit lightin one or more various color ranges, such as red, orange, and/or yellowrange. In some embodiments, NSs 601 and/or 600 may be synthesized toemit light in the green and/or yellow range. In some embodiments, NSs601 and/or 600 may be synthesized emit light in the blue, indigo,violet, and/or ultra-violet range. In some embodiments, NSs 601 and/or600 may be synthesized to have a primary emission peak wavelengthbetween about 605 nm and about 650 nm, between about 510 nm and about550 nm, or between about 300 nm and about 480 nm.

NSs 601 and/or 600 may be synthesized to display a high QY. In someembodiments, NSs 601 and/or 600 may be synthesized to display a QYbetween 80% and 95% or between 85% and 90%.

Thus, according to various embodiments, NSs 600 may be synthesized suchthat the presence of barrier layer 606 on NSs 601 does not substantiallychange or quench the optical emission properties of NSs 601.

Example Embodiments of a Nanostructure Film

FIG. 7 illustrates a cross-sectional view of a NS film 700, according toan embodiment. In some embodiments, phosphor films 236, 550, 552, and/or554 may be similar to NS film 700.

NS film 700 may include a plurality of barrier layer coated core-shellNSs 600 (FIG. 6) and a matrix material 710, according to an embodiment.NSs 600 may be embedded or otherwise disposed in matrix material 710,according to some embodiments. As used herein, the term “embedded” isused to indicate that the NSs are enclosed or encased within matrixmaterial 710 that makes up the majority component of the matrix. Itshould be noted that NSs 600 may be uniformly distributed throughoutmatrix material 710 in an embodiment, though in other embodiments NSs600 may be distributed according to an application-specific uniformitydistribution function. It should be noted that even though NSs 600 areshown to have the same size in diameter, a person skilled in the artwould understand that NSs 600 may have a size distribution.

In an embodiment, NSs 600 may include a homogenous population of NSshaving sizes that emit in the blue visible wavelength spectrum, in thegreen visible wavelength spectrum, or in the red visible wavelengthspectrum. In other embodiments, NSs 600 may include a first populationof NSs having sizes that emit in the blue visible wavelength spectrum, asecond population of NSs having sizes that emit in the green visiblewavelength spectrum, and a third population of NSs that emit in the redvisible wavelength spectrum.

Matrix material 710 may be any suitable host matrix material capable ofhousing NSs 600. Suitable matrix materials may be chemically andoptically compatible with NSs 600 and any surrounding packagingmaterials or layers used in applying NS film 700 to devices. Suitablematrix materials may include non-yellowing optical materials which aretransparent to both the primary and secondary light, thereby allowingfor both primary and secondary light to transmit through the matrixmaterial. In an embodiment, matrix material 710 may completely surroundeach of the NSs 600. The matrix material 710 may be flexible inapplications where a flexible or moldable NS film 700 is desired.Alternatively, matrix material 710 may include a high-strength,non-flexible material.

Matrix material 710 may include polymers and organic and inorganicoxides. Suitable polymers for use in matrix material 710 may be anypolymer known to the ordinarily skilled artisan that can be used forsuch a purpose. The polymer may be substantially translucent orsubstantially transparent. Matrix material 710 may include, but notlimited to, epoxies, acrylates, norbornene, polyethylene, poly(vinylbutyral):poly(vinyl acetate), polyurea, polyurethanes; silicones andsilicone derivatives including, but not limited to, amino silicone(AMS), polyphenylmethylsiloxane, polyphenylalkylsiloxane,polydiphenylsiloxane, polydialkylsiloxane, silsesquioxanes, fluorinatedsilicones, and vinyl and hydride substituted silicones; acrylic polymersand copolymers formed from monomers including, but not limited to,methylmethacrylate, butylmethacrylate, and laurylmethacrylate;styrene-based polymers such as polystyrene, amino polystyrene (APS), andpoly(acrylonitrile ethylene styrene) (AES); polymers that arecrosslinked with bifunctional monomers, such as divinylbenzene;cross-linkers suitable for cross-linking ligand materials, epoxideswhich combine with ligand amines (e.g., APS or PEI ligand amines) toform epoxy, and the like.

In some embodiments, matrix material 710 includes scattering microbeadssuch as TiO2 microbeads, ZnS microbeads, or glass microbeads that mayimprove photo conversion efficiency of NS film 700. In some embodiments,matrix material 710 may include light blocking elements such as lightblocking elements 238 and/or 548 described above with reference to FIGS.2-3 and 5.

In another embodiment, matrix material 710 may have low oxygen andmoisture permeability, exhibit high photo- and chemical-stability,exhibit favorable refractive indices, and adhere to outer surfaces ofNSs 600, thus providing an air-tight seal to protect NSs 600. In anotherembodiment, matrix material 710 may be curable with UV or thermal curingmethods to facilitate roll-to-roll processing.

According to some embodiments, NS film 700 may be formed by mixing NSs600 in a polymer (e.g., photoresist) and casting the NS-polymer mixtureon a substrate, mixing NSs 600 with monomers and polymerizing themtogether, mixing NSs 600 in a sol-gel to form an oxide, or any othermethod known to those skilled in the art.

According to some embodiments, the formation of NS film 700 may includea film extrusion process. The film extrusion process may include forminga homogenous mixture of matrix material 710 and barrier layer coatedcore-shell NSs such as NS 600, introducing the homogenous mixture into atop mounted hopper that feeds into an extruder. In some embodiments, thehomogenous mixture may be in the form of pellets. The film extrusionprocess may further include extruding NS film 700 from a slot die andpassing extruded NS film 700 through chill rolls. In some embodiments,the extruded NS film 700 may have a thickness less than about 75 μm, forexample, in a range from about 70 μm to about 40 μm, from about 65 μm toabout 40 μm, from about 60 μm to about 40 μm, or form about 50 μm toabout 40 μm. In some embodiments, NS film 700 has a thickness less thanabout 10 μm. In some embodiments, the formation of NS film 700 mayoptionally include a secondary process followed by the film extrusionprocess. The secondary process may include a process such asco-extrusion, thermoforming, vacuum forming, plasma treatment, molding,and/or embossing to provide a texture to a top surface of NS film 700.The textured top surface NS film 700 may help to improve, for exampledefined optical diffusion property and/or defined angular opticalemission property of NS film 700.

Example Embodiments of Luminescent Nanostructures

Described herein are various compositions having luminescentnanostructures (NSs). The various properties of the luminescentnanostructures, including their absorption properties, emissionproperties and refractive index properties, may be tailored and adjustedfor various applications.

The material properties of NSs may be substantially homogenous, or incertain embodiments, may be heterogeneous. The optical properties of NSsmay be determined by their particle size, chemical or surfacecomposition. The ability to tailor the luminescent NS size in the rangebetween about 1 nm and about 15 nm may enable photoemission coverage inthe entire optical spectrum to offer great versatility in colorrendering. Particle encapsulation may offer robustness against chemicaland UV deteriorating agents.

Luminescent NSs, for use in embodiments described herein may be producedusing any method known to those skilled in the art. Suitable methods andexample nanocrystals are disclosed in U.S. Pat. No. 7,374,807; U.S.patent application Ser. No. 10/796,832, filed Mar. 10, 2004; U.S. Pat.No. 6,949,206; and U.S. Provisional Patent Application No. 60/578,236,filed Jun. 8, 2004, the disclosures of each of which are incorporated byreference herein in their entireties.

Luminescent NSs for use in embodiments described herein may be producedfrom any suitable material, including an inorganic material, and moresuitably an inorganic conductive or semiconductive material. Suitablesemiconductor materials may include those disclosed in U.S. patentapplication Ser. No. 10/796,832, and may include any type ofsemiconductor, including group II-VI, group III-V, group IV-VI and groupIV semiconductors. Suitable semiconductor materials may include, but arenot limited to, Si, Ge, Sn, Se, Te, B, C (including diamond), P, BN, BP,BAs, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb,AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, ZnO, ZnS, ZnSe, ZnTe, CdS,CdSe, CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe, GeS, GeSe,GeTe, SuS, SnSe, SnTe, PbO, PbS, PbSe, PbTe, CuF, CuCl, CuBr, CuI,Si₃N₄, Ge₃N₄, Al₂O₃, (Al, Ga, In)₂ (S, Se, Te)₃, Al₂CO, and anappropriate combination of two or more such semiconductors.

In certain embodiments, the luminescent NSs may have a dopant from thegroup consisting of a p-type dopant or an n-type dopant. The NSs mayalso have II-VI or III-V semiconductors. Examples of II-VI or III-Vsemiconductor NSs may include any combination of an element from GroupII, such as Zn, Cd and Hg, with any element from Group VI, such as S,Se, Te and Po, of the Periodic Table; and any combination of an elementfrom Group III, such as B, Al, Ga, In, and Tl, with any element fromGroup V, such as N, P, As, Sb and Bi, of the Periodic Table.

The luminescent NSs, described herein may also further include ligandsconjugated, cooperated, associated or attached to their surface.Suitable ligands may include any group known to those skilled in theart, including those disclosed in U.S. Pat. No. 8,283,412; U.S. PatentPublication No. 2008/0237540; U.S. Patent Publication No. 2010/0110728;U.S. Pat. No. 8,563,133; U.S. Pat. No. 7,645,397; U.S. Pat. No.7,374,807; U.S. Pat. No. 6,949,206; U.S. Pat. No. 7,572,393; and U.S.Pat. No. 7,267,875, the disclosures of each of which are incorporatedherein by reference. Use of such ligands may enhance the ability of theluminescent NSs to incorporate into various solvents and matrixes,including polymers. Increasing the miscibility (i.e., the ability to bemixed without separation) of the luminescent NSs in various solvents andmatrixes may allow them to be distributed throughout a polymericcomposition such that the NSs do not aggregate together and therefore donot scatter light. Such ligands are described as “miscibility-enhancing”ligands herein.

In certain embodiments, compositions having luminescent NSs distributedor embedded in a matrix material are provided. Suitable matrix materialsmay be any material known to the ordinarily skilled artisan, includingpolymetic materials, organic and inorganic oxides. Compositionsdescribed herein may be layers, encapsulants, coatings, sheets or films.It should be understood that in embodiments described herein wherereference is made to a layer, polymeric layer, matrix, sheet or film,these terms are used interchangeably, and the embodiment so described isnot limited to any one type of composition, but encompasses any matrixmaterial or layer described herein or known in the art.

Down-converting NSs (for example, as disclosed in U.S. Pat. No.7,374,807) utilize the emission properties of luminescent nanostructuresthat are tailored to absorb light of a particular wavelength and thenemit at a second wavelength, thereby providing enhanced performance andefficiency of active sources (e.g., LEDs).

While any method known to the ordinarily skilled artisan may be used tocreate luminescent NSs, a solution-phase colloidal method for controlledgrowth of inorganic nanomaterial phosphors may be used. See Alivisatos,A. P., “Semiconductor clusters, nanocrystals, and quantum dots,” Science271:933 (1996); X. Peng, M. Schlamp, A. Kadavanich, A. P. Alivisatos,“Epitaxial growth of highly luminescent CdSe/CdS Core/Shell nanocrystalswith photostability and electronic accessibility,” J. Am. Chem. Soc.30:7019-7029 (1997); and C. B. Murray, D. J. Norris, M. G. Bawendi,“Synthesis and characterization of nearly monodisperse CdE (E=sulfur,selenium, tellurium) semiconductor nanocrystallites,” J Am. Chem. Soc.115:8706 (1993), the disclosures of which are incorporated by referenceherein in their entireties.

According to an embodiment, CdSe may be used as the NS material, in oneexample, for visible light down-conversion, due to the relative maturityof the synthesis of this material. Due to the use of a generic surfacechemistry, it may also possible to substitute non-cadmium-containingNSs.

In semiconductor NSs, photo-induced emission arises from the band edgestates of the NS. The band-edge emission from luminescent NSs competeswith radiative and non-radiative decay channels originating from surfaceelectronic states. X. Peng, et al., J Am. Chem. Soc. 30:7019-7029(1997). As a result, the presence of surface defects such as danglingbonds provide non-radiative recombination centers and contribute tolowered emission efficiency. An efficient and permanent method topassivate and remove the surface trap states may be to epitaxially growan inorganic shell material on the surface of the NS. X. Peng, et al.,J. Am. Chem. Soc. 30:701 9-7029 (1997). The shell material may be chosensuch that the electronic levels are type 1 with respect to the corematerial (e.g., with a larger bandgap to provide a potential steplocalizing the electron and hole to the core). As a result, theprobability of non-radiative recombination may be reduced.

Core-shell structures may be obtained by adding organometallicprecursors containing the shell materials to a reaction mixturecontaining the core NSs. In this case, rather than a nucleation eventfollowed by growth, the cores act as the nuclei, and the shells may growfrom their surface. The temperature of the reaction is kept low to favorthe addition of shell material monomers to the core surface, whilepreventing independent nucleation of nanocrystals of the shellmaterials. Surfactants in the reaction mixture are present to direct thecontrolled growth of shell material and to ensure solubility. A uniformand epitaxially grown shell may be obtained when there is a low latticemismatch between the two materials.

Example materials for preparing core-shell luminescent NSs may include,but are not limited to, Si, Ge, Sn, Se, Te, B, C (including diamond), P,Co, Au, BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN,InP, InAs, InSb, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, ZnO, ZnS,ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTc, BeS, BcSe, BcTe, MgS,MgSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, Pb Se, PbTe, CuP,CuCl, CuBr, CuI, Si₃N₄, Ge₃N₄, Al₂O₃, (Al, Ga, In)₂ (S, Se, Te)₃, AlCO,and shell luminescent NSs for use in the practice of the presentinvention include, but are not limited to, (represented as Core/Shell),CdSe/ZnS, InP/ZnS, InP/ZnSe, PbSe/PbS, CdSe/CdS, CdTe/CdS, CdTe/ZnS, aswell as others.

Luminescent NSs for use in the embodiments described herein may be lessthan about 100 nm in size, and down to less than about 2 nm in size andinvention absorb visible light. As used herein, visible light iselectromagnetic radiation with wavelengths between about 380 and about780 nanometers that is visible to the human eye. Visible light can beseparated into the various colors of the spectrum, such as red, orange,yellow, green, blue, indigo and violet. Blue light may comprise lightbetween about 435 nm and about 495 nm, green light may comprise lightbetween about 495 nm and 570 nm and red light may comprise light betweenabout 620 nm and about 750 nm in wavelength.

According to various embodiments, the luminescent NSs may have a sizeand a composition such that they absorb photons that are in theultraviolet, near-infrared, and/or infrared spectra. The ultravioletspectrum may comprise light between about 100 nm to about 400 nm, thenear-infrared spectrum may comprise light between about 750 nm to about100 μm in wavelength, and the infrared spectrum may comprise lightbetween about 750 nm to about 300 μm in wavelength.

While luminescent NSs of other suitable material may be used in thevarious embodiments described herein, in certain embodiments, the NSsmay be ZnS, InAs, CdSe, or any combination thereof to form a populationof nanocrystals for use in the embodiments described herein. Asdiscussed above, in further embodiments, the luminescent NSs may becore/shell nanocrystals, such as CdSe/ZnS, InP/ZnSe, CdSe/CdS orInP/ZnS.

Suitable luminescent nanostructures, methods of preparing luminescentnanostructures, including the addition of various solubility-enhancingligands, can be found in Published U.S. Patent Publication No.2012/0113672, the disclosure of which is incorporated by referenceherein in its entirety.

It is to be understood that while certain embodiments have beenillustrated and described herein, the claims are not to be limited tothe specific forms or arrangement of parts described and shown. In thespecification, there have been disclosed illustrative embodiments and,although specific terms are employed, they are used in a generic anddescriptive sense only and not for purposes of limitation. Modificationsand variations of the embodiments are possible in light of the aboveteachings. It is therefore to be understood that the embodiments may bepracticed otherwise than as specifically described.

What is claimed is:
 1. A display device comprising: a backlight unitcomprising a light source configured to emit a primary light in a firstwavelength region of an electromagnetic (EM) spectrum; and a liquidcrystal display (LCD) module comprising a pixel having: a firstsub-pixel having a first emissive surface configured to emit a firstlight, having a first luminance, in a second wavelength region of the EMspectrum, wherein the first sub-pixel comprises a first phosphor filmdisposed on a substrate and a first filter element disposed on the firstphosphor film; a second sub-pixel having a second emissive surfaceconfigured to emit a second light, having a second luminance, in a thirdwavelength region of the EM spectrum, wherein the first, second, andthird wavelength regions are different from each other, wherein thesecond sub-pixel comprises a second phosphor film disposed on thesubstrate and a second filter element disposed on the second phosphorfilm, and wherein the first and second phosphor films are differentregions of a continuous phosphor film and the first and second filterelements are different regions of a continuous filter element disposedon the continuous phosphor film; and a third sub-pixel having a thirdemissive surface configured to emit a third light, having a thirdluminance, in the first wavelength region of the EM spectrum, whereinthe third luminance is greater than the first luminance and the secondluminance, wherein the third sub-pixel comprises an opticallytransparent film disposed on the substrate, and wherein an area of thethird emissive surface is smaller than an area of the first emissivesurface and an area of the second emissive surface.
 2. The displaydevice of claim 1, wherein a ratio between the areas of the first,second, and third emissive surfaces ranges from about 2:2:1 to about6:6:1.
 3. The display device of claim 1, wherein a ratio between theareas of the first, second, and third emissive surfaces is about 4:4:1.4. The display device of claim 1, wherein the areas of the first,second, and third emissive surfaces are different from each other. 5.The display device of claim 1, wherein the third light comprises aportion of the primary light.
 6. The display device of claim 1, wherein:the first phosphor film is configured to convert a first portion of theprimary light to emit the first light; and the first filter element isoptically coupled to the first phosphor film and is configured to allowthe first light to pass through the first filter element and to block anunconverted portion of the primary light from passing through the firstfilter element.
 7. The display device of claim 6, wherein a surface ofthe first filter element comprises the first emissive surface.
 8. Thedisplay device of claim 1, wherein: the first phosphor film isconfigured to convert a first portion of the primary light to emit thefirst light; and a surface of the first phosphor film comprises thefirst emissive surface.
 9. The display device of claim 1, wherein: thesecond phosphor film is configured to convert a second portion of theprimary light to emit the second light; and the second filter element isoptically coupled to the second phosphor film and is configured to allowthe second light to pass through the second filter element and to blockan unconverted portion of the primary light from passing through thesecond filter element.
 10. The display device of claim 9, wherein asurface of the second filter element comprises the second emissivesurface.
 11. The display device of claim 1, wherein: the first andsecond phosphor films comprise first and second matrices, respectively;and the first and second filter elements are embedded in the first andsecond matrices, respectively.
 12. The display device of claim 1,wherein each of the first and second filter elements comprisesscattering particles having titanium oxide, zinc oxide, zinc sulfide,silicone, or a combination thereof.
 13. The display device of claim 1,wherein: the first phosphor film comprises a first population ofluminescent nanostructures configured to emit the first light in awavelength region ranging from about 620 nm to about 750 nm; and thesecond phosphor film comprises a second population of luminescentnanostructures configured to emit the second light in a wavelengthregion ranging from about 495 nm to about 570 nm.
 14. The display deviceof claim 1, wherein: the second phosphor film is configured to convert asecond portion of the primary light to emit the second light; and asurface of the second phosphor film comprises the second emissivesurface.
 15. The display device of claim 1, wherein the third sub-pixelexcludes luminescent nanostructures.
 16. The display device of claim 1,wherein the LCD module further comprises: a first polarizing filterconfigured to polarize the primary light; a liquid crystal solutionlayer configured to adjust an angle of polarization of the polarizedprimary light; and a second polarizing filter, disposed between theliquid crystal solution layer and the first, second, and thirdsub-pixels, configured to control transmission of the polarized primarylight from the liquid crystal solution layer to the first, second, andthird sub-pixels.
 17. The display device of claim 1, further comprisingan optical cavity, wherein the light source is positioned within theoptical cavity.
 18. The display device of claim 1, further comprising alight guide plate, wherein the light source is externally coupled to thelight guide plate.
 19. A display device comprising: a first sub-pixelhaving a first emissive surface configured to emit a first light, havinga first luminance, in a first wavelength region of an electromagnetic(EM) spectrum, wherein the first sub-pixel comprises a first phosphorfilm disposed on a substrate and a first filter element disposed on thefirst phosphor film; a second sub-pixel having a second emissive surfaceconfigured to emit a second light, having a second luminance, in asecond wavelength region of the EM spectrum; and a third sub-pixelhaving a third emissive surface configured to emit a third light, havinga third luminance, in a third wavelength region of the EM spectrum,wherein the third luminance is greater than the first luminance and thesecond luminance, wherein the third sub-pixel comprises an opticallytransparent film disposed on the substrate and the optically transparentfilm comprises scattering particles, and wherein the first, second, andthird wavelength regions are different from each other, and wherein anarea of the third emissive surface is smaller than an area of the firstemissive surface and an area of the second emissive surface.
 20. Thedisplay device of claim 19, wherein: the first sub-pixel furthercomprises a first light source configured to emit a first primary lightin the third wavelength region; the second sub-pixel further comprises asecond light source configured to emit a second primary light in thethird wavelength region; and the third sub-pixel further comprises athird light source configured to emit a third primary light in the thirdwavelength region.
 21. The display device of claim 20, wherein each ofthe first, second, and third light sources comprises an organic lightemitting diode (OLED).
 22. The display device of claim 19, wherein aratio between the areas of the first, second, and third emissivesurfaces ranges from about 2:2:1 to about 6:6:1.
 23. The display deviceof claim 19, wherein a ratio between the areas of the first, second, andthird emissive surfaces is about 4:4:1.
 24. The display device of claim19, wherein the areas of the first, second, and third emissive surfacesare different from each other.
 25. The display device of claim 20,wherein the third light comprises a portion of the third primary light.26. The display device of claim 20, wherein the first sub-pixel furthercomprises: the first phosphor film configured to convert a portion ofthe first primary light to emit the first light; and the first filterelement, optically coupled to the first phosphor film, configured toallow the first light to pass through the first filter element and toblock an unconverted portion of the first primary light from passingthrough the first filter element.
 27. The display device of claim 26,wherein a surface of the first filter element comprises the firstemissive surface.
 28. The display device of claim 20, wherein: the firstsub-pixel further comprises a first phosphor film configured to converta portion of the first primary light to emit the first light; and asurface of the first phosphor film comprises the first emissive surface.29. The display device of claim 20, wherein the second sub-pixel furthercomprises: a second phosphor film configured to convert a portion of thesecond primary light to emit the second light; and a second filterelement, optically coupled to the second phosphor film, configured toallow the second light to pass through the second filter element and toblock an unconverted portion of the second primary light from passingthrough the second filter element.
 30. The display device of claim 29,wherein a surface of the second filter element comprises the secondemissive surface.
 31. The display device of claim 29, wherein: the firstphosphor film comprises a first population of luminescent nanostructuresconfigured to emit the first light in a wavelength region ranging fromabout 620 nm to about 750 nm; and the second phosphor film comprises asecond population of luminescent nanostructures configured to emit thesecond light in a wavelength region ranging from about 495 nm to about570 nm.
 32. The display device of claim 20, wherein: the secondsub-pixel further comprises a second phosphor film configured to converta portion of the second primary light to emit the second light; and asurface of the second phosphor film comprises the second emissivesurface.
 33. The display device of claim 19, wherein the third sub-pixelexcludes luminescent nanostructures.
 34. A display device comprising: afirst emissive surface configured to emit a first light, having a firstluminance, in a first wavelength region of an electromagnetic (EM)spectrum; a second emissive surface configured to emit a second light,having a second luminance, in a second wavelength region of the EMspectrum; and a third emissive surface configured to emit a third light,having a third luminance, in a third wavelength region of the EMspectrum, wherein the third luminance is greater than the firstluminance and the second luminance, wherein the first, second, and thirdwavelength regions are different from each other, wherein the first andsecond emissive surfaces are different regions of a continuous filterelement, and wherein the areas of the first, second, and third emissivesurfaces are different from each other.
 35. The display device of claim34, wherein a ratio between the areas of the first, second, and thirdemissive surfaces ranges from about 2:2:1 to about 6:6:1.
 36. Thedisplay device of claim 34, wherein a ratio between the areas of thefirst, second, and third emissive surfaces is about 4:4:1.
 37. Thedisplay device of claim 34, further comprising: a first phosphor filmhaving a first surface that comprises the first emissive surface; asecond phosphor film having a second surface that comprises the secondemissive surface; and a third phosphor film having a third surface thatcomprises the third emissive surface.
 38. The display device of claim34, wherein the first, second, and third emissive surfaces are differentregions of a pixel of the display device.
 39. The display device ofclaim 34, further comprising a light source configured to emit a primarylight in the third wavelength region.
 40. The display device of claim34, wherein: the first wavelength region ranges from about 620 nm toabout 750 nm; the second wavelength region ranges from about 495 nm toabout 570 nm ; and the third wavelength region ranges from about 435 nmto about 495 nm.
 41. The display device of claim 34, further comprising:a first filter element having a first surface that comprises the firstemissive surface; a second filter element having a second surface thatcomprises the second emissive surface; and a third filter element havinga third surface that comprises the third emissive surface.
 42. Thedisplay device of claim 41, wherein the first, second, and third filterelements are disposed on a same surface plane.
 43. The display device ofclaim 37, wherein: the first phosphor film is configured to convert afirst portion of a primary light to emit the first light; the secondphosphor film is configured to convert a second portion of the primarylight to emit the second light; and the third phosphor film isconfigured to convert a third portion of the primary light to emit thethird light.
 44. The display device of claim 37, wherein the first,second, and third phosphor films are disposed on a same surface plane.